Impact ionisation measurement and modelling of long wavelength avalanche photodiodes

Impact ionisation coefficients are measured in In_0_._5_3Ga_0_._4_7As and excess noise characteristics are measured in sub-micron ln_0_._5_2Al_0_._4_8As. Photomultiplication measurements performed on a series of In_0_._5_3Ga_0_._4_7As p-i-n diodes are reported. Taking careful account of factors which could give rise to erroneous results at low fields, ln_0_._5_3Ga_0_._4_7As ionisation coefficients are deduced at room temperature as a function of electric field. The results confirm the low field ionisation behaviour of #alpha# and the conventional field dependence of #beta#. Excess avalanche noise factors of In_0_._5_2Al_0_._4_8As p-i-n diodes, with i-region thicknesses ranging from 1.0#mu#m to 0.1#mu#m, are reported. The results indicate effective #beta#/#alpha# values lying between 0.15 and 0.23, comparable with or lower than the values reported in the only other systematic study of excess noise characteristics in ln_0_._5_2Al_0_._4_8As. The effects of dead space, enhanced speed to ionisation of early ionising carriers and carrier diffusion on multiplication-limited bandwidth are studied in this work via modelling. The degradation of bandwidth due to the presence of dead space, predicted by other authors, was investigated using the Random Path Length model. It was found that dead space increases the order of carrier groups involved in multiplication, and hence the length of the multiplication chains, as impact ionisation events initiated by feedback carriers become more important. This degrades the improvement in bandwidth expected from reducing the multiplication layer thickness. To study the effects of enhanced speed to ionisation of early ionising carriers and of carrier diffusion on the avalanche time response, a technique has been developed for calculating the probability distribution function (pdf) of avalanche duration using general models for pdfs of ionisation in space and time and also for carrier transport. While diffusion plays only a minor role, the speed enhancement of carriers to ionisation events early in their trajectories is found to speed up the avalanche process significantly in short devices. (author)SIGLEAvailable from British Library Document Supply Centre- DSC:DXN060420 / BLDSC - British Library Document Supply CentreGBUnited Kingdo